Vibrio cholerae, which lives in association with plankton in brackish, temperate waters the world over, is the causative agent of endemic and epidemic cholera. Hallmarks of the disease include prodigious watery diarrhea resulting from the action of secreted cholera toxin (CT), and infrequent but deadly explosive epidemics. The strong link between explosive epidemics and human crowding accompanied with untreated drinking water suggests a very efficient mode of fecal-oral transmission. We have discovered a heightened state of transmissibility of stool V. cholerae (referred to simply as "hyperinfectivity"), which persists even after shedding into water reservoirs. Knowledge of the molecular basis for this phenotype, and a general characterization of this transmissible form of V. cholerae, would contribute to the design of vaccines to prevent cholera at the initial stage of infection. Aim 1 of this proposal will use transcriptional profiling and proteomics to help define this transmissible form. Spotted DNA microarrays will be used to determine the transcriptome of stool V. cholerae incubated in pond water, and this will be compared to that of fresh stool V. cholerae to identify potential differences. The results will be validated by quantitatively assaying the steady state mRNA and protein levels from select genes. Microscopy and transcriptome data on stool V. cholerae predict a bacterial state of motility working in the absence of chemotactic signaling. This counterintuitive state is hypothesized to be responsible, at least in part, for the hyperinfective phenotype. In Aim 2 of this proposal, quantitative immunodetection using paralog-specific antisera will be used to test for reduced expression of all three CheW linker proteins and all three CheR methytransferases in fresh and pond water-incubated stool V. cholerae, as is predicted by current transcriptome data. In addition, capillary tube chemotaxis assays will be performed directly on V. cholerae from these samples to substantiate this hypothesis. Aim 2 will also test a second hypothesis, that ToxR regulated factors, which are essential for pathogenesis, are not playing a role in the hyperinfectious state. Finally, Aim 3 will use mutation and infectivity analyses to determine if other metabolic, physiologic or phenotypic properties of the bacteria contribute to the hyperinfective phenotype or, alternatively, to colonization of an environmental planktonic host, Anabaena variabilis. These studies will establish a basis for understanding the hyperinfective phenotype, and the properties in general, that are exhibited by fresh and pond water-incubated stool V. cholerae. In turn, this knowledge will enhance our understanding of transmission of this and perhaps other water-borne pathogens, it will aid in the development of new cholera vaccines that target the antigens of 'incoming' vibrios, and it may suggest new approaches for the prevention of the dissemination of this lethal organism.